This application claims the priority of German Application No. 198 52 227.4, filed Nov. 12, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method, a selector switch and a selector device, particularly in the case of a vehicle, for secure position detection of the selector switch, which can be operated in at least two positions.
A great number of selector switches are known in many fields of application. Their operation may trigger a mechanical, hydraulic, pneumatic or electric reaction. The present case relates to selector switches, which can be operated in at least two positions and emit an electric signal. The electrical signal is assigned to the respective position of the switch. The assignment (also known as coding) of the operating position to the corresponding reaction may be of an analog or digital nature. In the case of digital coding, a specific bit pattern, generated, for example, by the operation of switching elements, is assigned to each selector switch position.
Selector switches are known, in the case of which a specific electric switch, for example, an end position switch, is operated. The switch signal indicates the selector switch position to a control unit.
Within the wide range of application of selector switches, there are also those which supply particularly safety-relevant information. In the case of these selector switches, a special intrinsic safety and operability is particularly important. In the case of a motor vehicle, which has an electronically shiftable transmission, a transmission selector switch is but one example. Several switching positions must be recognized in a safe and reliable manner and must be transmitted to an electronic transmission control unit.
It is an object of the present invention to provide a method, a selector switch and a selector device, which permit secure position detection of a position taken up by the selector switch.
This object is achieved by a method for secure position detection, wherein a first switch position code composed of at least two bits is assigned to each selector switch position. The first switch position code is generated by a number of switches, which correspond to the number of bits of the code. A coding is used whereby the selector switch position assigned to a code is redundantly present in a code word as a second switch position code. A decoding algorithm is used which corresponds to the coding such that the redundant selector switch positions assigned to the code word are determined. From a comparison of the selector switch positions determined from the code word, a conclusion is drawn with respect to correct or erroneous position detection of the selector switch.
In another advantageous embodiment, the object is achieved by connecting the redundant coding via an imaging rule. By means of the imaging rule, the redundant selector switch position is determined from a detected selector switch position. From a comparison of the selecting position generated by means of the imaging rule and the detected redundant selecting position, a conclusion is drawn with respect to the correct or erroneous position detection of the selector switch.
The object is further achieved for a selector switch in a motor vehicle, wherein the selector switch positions are electrically detected by means of a defined number of switches. The switches supply information assigned to a respective selector switch position and combined to a respectively assigned code word. The code words redundantly contain the selector lever position as a second switch position code.
In a selecting device for achieving the object, a control device is provided. The selector switch supplies the code word to the control device. The control device is constructed to implement the method and, corresponding to the selector switch position reported by the selector switch and tested, the control device supplies a corresponding signal to a controllable unit.
The required intrinsic safety is basically achieved by using a redundant code, which therefore permits error recognition. A specific code word is bi-uniquely assigned to a selector switch position. By an evaluation of the redundant information in the code word, a conclusion can be drawn concerning an erroneous position detection.
Such methods are partially already known from other fields of applicationxe2x80x94for example, for ensuring correct data transmission. The degree of redundancy and thus the used codes depend on the intrinsic safety demands on the selector switch. On the whole, using a redundant digital code, a selector switch can advantageously be implemented having an arbitrarily high intrinsic safety.
It is also essential to the invention that valid code words, as the result of the coding rule, are imaged by a constructive conversion to a geometrical switch arrangement such that not only a bi-uniquely valid code word is assigned from the used coding space, but also that this code word at least twice additionally contains the selector switch position. By decoding the code word via a code-conforming algorithm, the redundancy contained in the code word becomes effective during the testing of the selector switch position.
The present invention is described with respect to two different embodiments. According to a first embodiment, the at least two selector switch positions are determined. The two positions are redundantly determined in the code word and are compared with one another. According to the second embodiment, the redundant selector switch position is theoretically determined from a selector switch position using a known imaging rule. The theoretical position is compared with the actually present second selector switch position.
A special embodiment is obtained by using the Hamming Code. However, the use of the Hamming Code is not meant to limit the scope of the invention.
According to an advantageous embodiment, a code word (composed of a data part (first switch position code) and a test part second switch position code)) is assigned to each selector switch position. Each code word in each selector switch position is generated by a number of switches corresponding to the number of bits of the code word, the data part already indicating an unambiguous selector switch position. The test part of each code word is obtained from a defined imaging rule from the data part. If then the test part actually generated by the switches is compared with the test part calculated from the data part according to the defined imaging rule, a conclusion can be drawn with respect to a correct or faulty position detection at the selector switch.
According to an expanded Hamming Code, an expanded test part can be provided in the case of the code word, the information of the test part resulting from a defined combination of the data and the test parts.
By means of the expanded Hamming Code, double fault recognition is possible. Although a double fault correction cannot be carried out, the vehicle driver can be informed of the presence of a corresponding fault and the corresponding precautionary measures can be taken.
By means of the normal Hamming Code, a single fault detection is possible. In this case, while the imaging rule is defined correspondingly (for example, an EXCLUSIVE-OR linking of the data part information), not only the existence of a single fault but also its position can be detected.
According to the selected Hamming distance (dmin=3; dmin=4), at every change of the switching position of the selector switch, a defined number of shifting operations take place. For this purpose, the code words must be selected correspondingly from the number of available possible code words (code word space). This effect can be utilized for determining asynchronous conditions during the shifting operation. When a Hamming distance of dmin=4 is selected, a new switching position can unambiguously be determined already after three bit changes. The approach may be that a code word will only be considered after three bit changes have taken place. For every position change, Boolean equations can be established and the changed bits can be compared with a Boolean operation table of the switching conditions. In the case of a corresponding conformity, a correct switch position was found. As a result of the last-mentioned measure, an error value of up to the fourth order can, in addition, be corrected. However, it is a disadvantage in this case that no localization of the defective signal paths is possible in the first step.
The two test parts (i.e., the detected test part and the calculated test part), are formed by way of an EXCLUSIVE-OR linkagexe2x80x94a so-called syndrome. In the event of detecting a single error, a stored syndrome table can supply information on the position of the error. Furthermore, when a code word with an expanded test part is used, while taking into account the expanded test part in the comparison of the tests parts, particularly of the syndrome, a stored table can rapidly and reliably indicate the presence of a double error.
The selector switch according to the present invention is constructed such that a number of switches generate the code word. The switches are assigned to the data parts or test parts (also an expanded test part). Care must be taken that the switches for the test parts are arranged and wired such that, at each selector switch position, the information of each test part is obtained in accordance with the defined imaging rule. Sliding contacts, Hall sensors or other switches can be used as the switches. The use of Hall sensors was found to be particularly advantageous. In this case, magnets for the Hall sensors assigned in each case to a specific switch can be arranged corresponding to a desired gear shifting gate and corresponding to an assignment of the code word information/selector switch position.
All Hall sensors assigned to the corresponding switches can be combined in a certain arrangement, opposite which a respective matching magnet array is situated. In this context, reference is made to the following embodiments.
A toggle switch, push button key or lever, or any other switch can be used as the selector switch.
In another advantageous embodiment according to the invention, a selecting device comprises a selector switch as well as a control device. The selector switch is constructed as discussed above. The control device is suitable for receiving and analyzing the transmitted code words and emits a signal to a unit to be controlled. This signal is reported by a selector. switch and is tested.
On the whole, the present invention provides the possibility of reliably detecting a selector switch position selected from several switching positions and determining and possibly eliminating errorsxe2x80x94at least of a certain order. When selector switches are used on which particularly high demands are made concerning the intrinsic safety and reliability, the present invention meets these demands by implementing redundant systems.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.